This invention relates generally to injectors for rocket engines, and, more particularly to a dual manifold high performance throttleable injector.
The purpose of any rocket engine injector is to provide a means whereby the propellants; that is, the oxidizer and fuel are uniformly distributed, thoroughly mixed and atomized prior to vaporizing, igniting and combusting. Complete combustion must take place within a minimum of chamber volume for optimum efficiency. Injectors normally incorporate a manifolding system in which the propellants are physically distributed in specific areas adjacent to each other on the backside of the injector face. Orifices are then located into these areas to provide a "pattern" of oxidizer and fuel streams or sprays. The injection pattern is usually such that the fuel is in close proximity to the oxidizer at the proper mixture ratio; that is, the flow rate of the oxidizer with respect to that of the fuel must be constant at any incremental area of the injector face. The pattern of propellant orifices thus created, primarily determines the effectiveness of the combustion process.
In rocket engine injectors for introducing fuel and oxidant fluids into combustion chambers, the injectors have generally been classified as to the type of method of mixing or atomizing the fluids, and designated as impingement, spray, splash, premixing or showerhead pattern types. The impingement type of injectors consist of a number of separate holes arranged in such a manner that the resulting propellant streams of the fuel and oxidant intersect each other whereby a full stream of the fuel will impinge the oxidizer stream and break up into small droplets. In the spray or splash types of injectors, the injectors provide conical, cylindrical, or other type of spray sheets of propellant fluids which intersect each other and thereby atomize and mix. The premixing or non-impinging injector is one wherein the fuel and the oxidizer do not impinge but mix largely by diffusion of the propellant vapors and turbulence, that is, fine particles of fuel mix with oxidizer.
These prior methods of propellant mixing and atomization have certain inherent disadvantages. In the impingement type of injectors, for example, the droplet size is of considerable significance in that there is not always assurance of atomization and it is possible that the stream of oxidant will remain uncombined with the fuel or be misdirected against the combustion chamber wall. The spray, splash, and premixing type of injectors are not capable of providing the fine atomization and intimate mixing which is required in order to insure proper combustion at various flow rates of the oxidant and fuel into the combustion chamber for various rocket thrust levels.
U.S. Pat. No. 3,615,054 describes an injector which provides good atomization and intimate mixing over a wide range in flow rate of the oxidant and fuel into the combustion chamber by providing means for introducing the two fluids into the chamber whereby there is intimate mixing in the combustion chamber which is provided by an injector constructed of a plurality of discrete thin platelets or wafers joined together to form a unitary structure or module.
Unfortunately, even the injector set forth in U.S. Pat. No. 3,615,054 is deficient when it comes to yielding high performance over an extremely wide range of propellant flow rates. A major problem associated with throttling conventional liquid rocket engines by simply decreasing propellant flow by means of valves, is that the injector pressure drop decreases very rapidly as flow is reduced. As the systems hydraulic "stiffness" (injector pressure drop/chamber pressure) decreases rapidly, the inception of low frequency coupled combustion chamber/feed system instabilities become more likely.